ut 5to about 18 carbon atoms, and L is a leaving group, the conjugate acid of which has a pK.sub..alpha. in the range of about 6 to about 13.Nakagawa et al., U.S. Pat No. 3,960,743, issued Jun. 1, 1976, discloses an activating agent represented by the formula ##STR5## wherein R stands for an alkyl group having 1 to 15 carbon atoms, a halogen- or hydroxyl-substituted alkyl grouphaving 1 to 16 carbo